Ultrafiltration (UF) is a membrane process which lies between microfiltration (MF) and nanofiltration (NF). The pore sizes of such membranes are typically within the range of about 2 to 100 nm [1]. Upon applying a driving force of 1-3 bar, this membrane process results in the retention of macromolecules and colloids. While these larger molecules are retained by the membrane, smaller molecules along with the solvent permeate freely. As such, the mechanism of UF depends mainly on size exclusion. This process has been widely applied in industries, such as juice and beverage [2, 3] dialysis [4], and water purification
The ideal UF membranes should have the characteristics of: (1) hydrophilicity and high water flux; (2) highly porous with sponge-like (no macrovoid) and interconnected pore structures; (3) sufficient mechanical strength with good long term membrane stability.
Most UF membranes are prepared via the phase inversion process to form asymmetric membranes from materials such as polysulfone (PSU) [5], poly(vinylidene) fluoride (PVDF) [6], cellulose acetate (CA) [7] and polyimide (PI) [8]. Among these, polyarylsulfones are known for their chemical and mechanical resistance, thermal stability as well as ability to withstand wide ranges of temperature and corrosive environment [9]. However, in account of the hydrophobic properties of some abovementioned polymers, i.e. PSU and PVDF, UF membranes made from these polymers are subject to poor wettability by an aqueous media, macrovoids formation as well as fouling tendency. As a result, there is the need to include additives which commonly act as hydrophilizing and pore forming agents, i.e. polyethylene glycol (PEG) [10,11], polyvinylpyrollidone (PVP) to such polymer materials for UF applications.
There is a need of advanced UF separation techniques making use of membranes with an excellent chemical resistance and thermal stability
In the previous works, sulfonated PPSUs with a functionality of 0.8 to 2.5 meq/g [12] and polymer blends of CA and sulfonated PPSU [13] have been applied for electro dialysis. However, UF membranes consisting of directly sulfonated material prepared without blending with other polymer materials with lower functionality would be highly desirable.